Coatings comprising carbon nanotubes and methods for forming same

ABSTRACT

An electrically conductive film is disclosed. According to one embodiment of the present invention, the film includes a plurality of single-walled nanotubes having a particular diameter. The disclosed film demonstrates excellent conductivity and transparency. Methods of preparing the film as well as methods of its use are also disclosed herein.

REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/278,419 entitled “Electrodissipative Transparent Coatings ComprisingSingle-Wall Nanotubes and Methods for Forming Same” filed Mar. 26, 2001,U.S. Provisional Application No. 60/311,810 entitled “EMI IR Materials”filed Aug. 14, 2001, U.S. Provisional Application No. 60/311,811entitled “Biodegradable Film” filed Aug. 14, 2001, and U.S. ProvisionalApplication No. 60/311,815 entitled “EMI Optical Materials” filed Aug.14, 2001, each of which is entirely and specifically incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates electrically conductive coatings.

More particularly, the invention relates to transparent electricallyconductive coatings comprising carbon nanotubes.

2. Description of the Related Art

Electrically conductive transparent films are known in the art. Ingeneral, such films are generally formed on an electrical insulatingsubstrate by either a dry or a wet process. In the dry process, PVD(including sputtering, ion plating and vacuum deposition) or CVD is usedto form a conductive transparent film of a metal oxide type, e.g.,tin-indium mixed oxide (ITO), antimony-tin mixed oxide (ATO),fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (FZO). In thewet process, a conductive coating composition is formed using anelectrically conductive powder, e.g., one of the above-described mixedoxides and a binder. The dry process produces a film having both goodtransparency and good conductivity. However, it requires a complicatedapparatus having a vacuum system and has poor productivity. Anotherproblem of the dry process is that it is difficult to apply to acontinuous or big substrate such as photographic films or show windows.

The wet process requires a relatively simple apparatus, has highproductivity, and is easy to apply to a continuous or big substrate. Theelectrically conductive powder used in the wet process is a very finepowder having an average primary particle diameter of 0.5 μm or less soas not to interfere with transparency of the resulting film. To obtain atransparent coating film, the conductive powder has an average primaryparticle diameter of half or less (0.2 μm) of the shortest wave ofvisible light so as not to absorb visible light, and to controllingscattering of the visible light.

The development of intrinsically conductive organic polymers andplastics has been ongoing since the late 1970's. These efforts haveyielded conductive materials based on polymers such as polyanaline,polythiophene, polypyrrole, and polyacetylene. (See “ElectricalConductivity in Conjugated Polymers.” Conductive Polymers and Plasticsin Industrial Applications”, Arthur E. Epstein; “Conductive Polymers.”Ease of Processing Spearheads Commercial Success. Report from TechnicalInsights. Frost & Sullivan; and “From Conductive Polymers to OrganicMetals.” Chemical Innovation, Bernhard Wessling.

A significant discovery was that of carbon nanotubes, which areessentially single graphite layers wrapped into tubes, either singlewalled nanotubes (SWNTs) or double walled (DWNTs) or multi walled(MWNTs) wrapped in several concentric layers. (B. I. Yakobson and R. E.Smalley, “Fullerene Nanotubes: C_(1,000,000) and Beyond”, AmericanScientist v. 85, July-August 1997). Although only first widely reportedin 1991, (Phillip Ball, “Through the Nanotube”, New Scientist, 6 July1996, p. 28-31.) carbon nanotubes are now readily synthesized in gramquantities in the laboratories all over the world, and are also beingoffered commercially. The tubes have good intrinsic electricalconductivity and have been used in conductive materials.

U.S. Pat. No. 5,853,877, the disclosure of which is incorporated byreference in its entirety, relates to the use of chemically-modifiedmultiwalled nanotubes (MWNT). The coating and films disclosed in U.S.Pat. No. 5,853,877 are optically transparent when formed as a very thinlayer. As the thickness of the films increases to greater than about 5μm, the films lose their optical properties.

U.S. Pat. No. 5,853,877 also relates to films that are formed with andwithout binders. The films include binders with a very high nanotubeconcentration and are extremely thin in order to maintain the opticalproperties. For example, the patent discloses a film with 40% wt MWNTloading to get good ESD conductivities.

U.S. Pat. No. 5,908,585, the disclosure of which is incorporated byreference in its entirety, relates the use of two conductive additives,both MWNT and an electrically conductive metal oxide powder.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for an electrically conductive filmcomprising nanotubes with a particular diameter that overcome thosedrawbacks of the related art.

Accordingly, in a preferred embodiment, the invention provideselectrostatic dissipative transparent coatings comprising nanotubes.

Accordingly, in another preferred embodiment, the invention provides anelectrically conductive film comprising: a plurality of nanotubes withan outer diameter of less than 3.5 nm.

In another preferred embodiment, the invention provides a method formaking an electrically conductive film of claim 1 comprising: providinga plurality of nanotubes with an outer diameter of less than 3.5 nm; andforming a film of said nanotubes on a surface of a substrate.

In another preferred embodiment, the invention provides a multi-layeredstructure comprising: an electrically conductive film, and a polymericlayer disposed on at least a portion of said electrically conductivefilm.

In another preferred embodiment, the invention provides dispersions ofnanotubes suitable for forming films and other compositions. Suchcompositions may contain additional conductive, partially conductive ornon-conductive materials. The presence of nanotubes reduces themanufacturing costs of conventional materials that do not containnanotubes while increasing product effectiveness, preferably productconductivity. Compositions may be in any form such as a solid or liquid,and is preferably a powder, a film, a coating, an emulsion, or mixeddispersion.

Other objects, features and advantages of the present invention willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and the specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate a presently preferred embodimentof the invention, and, together with the general description given aboveand the detailed description of the preferred embodiment given below,serve to explain the principles of the invention. Thus, for a morecomplete understanding of the present invention, the objects andadvantages thereof, reference is now made to the following descriptionstaken in connection with the accompanying drawings in which:

FIG. 1 is a plot of conductivity verses thickness for SWNT coatingsaccording to one embodiment of the present invention;

FIG. 2 depicts a plot of the affect of high humidity on an ESD coatingover an extended period of time according to one embodiment of thepresent invention;

FIG. 3 depicts a plot of surface resistivity versus temperature data forSi-DETA-50-Ti with 0.30% SWNT cast on to a glass slide according to oneembodiment of the present invention;

FIG. 4 depicts a plot of surface resistivity versus temperature data forSi-DETA-50-Ti with 0.20% SWNT cast on to a glass slide according to oneembodiment of the present invention;

FIG. 5 depicts a plot of surface resistivity versus test voltage datafor Si-DETA-50-Ti with 0.3% SWNT cast on to a glass slide according toone embodiment of the present invention; and

FIG. 6 depicts the percent nanotubes cast on glass slides labeled withresistance measurements according to one embodiment of the presentinvention.

FIG. 7 depicts advantages of SWNTs used to impart electrical propertiesto films.

FIG. 8 depicts results showing how each of the three films resistivity(@500V) varied with temperature from −78 to +300° C.

FIG. 9 depicts resistivity in Ohms/Sq. for 1 mil POLYIMIDE-1 film asvoltage is reduced.

FIG. 10 depicts tensile properties for POLYIMIDE-1, POLYIMIDE-2, and TPOresins with and without nanotubes.

FIG. 11 depicts CTE Data on POLYIMIDE-1, POLYIMIDE-2, and TPO 1 milfilms with and without 0.1% SWnTs.

FIG. 12 depicts a POLYIMIDE-1 coating with 0.3% SWNTs @ 1.5 μm thick,slide is tilted off the paper/pavement by piece of mica, and isilluminated by sunlight. Stats: 96% T, 0.6% Haze, resistivity 3×10⁸Ohms/sq.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention and its advantagesare understood by referring to the Figs. of the drawings, wherein likenumerals being used for like and corresponding parts of the variousdrawings.

The instant invention relates to particular electrically conductivefilms comprising nanotubes and methods of forming the same. The instantfilms comprising nanotubes demonstrate advantageous light transmissionsover those materials comprising nanotubules disclosed heretofore. Inthis connection the instant invention relies on nanotubes with aparticular diameter which impart surprising advantages over those filmsdisclosed in the prior art.

In relation to the above, it has surprisingly been found that nanotubeswith an outer diameter of less than 3.5 nm are particularly goodcandidates to impart conductivity and transparency at low loading doses.These nanotubes can exhibit electrical conductivity as high as copper,thermal conductivity as high as diamond, strength 100 times greater thansteel at one sixth the weight, and high strain to failure. However,heretofore, there has been no report of such nanotubes in anelectrically conductive and transparent film.

Nanotubes are known and have a conventional meaning. (R. Saito, G.Dresselhaus, M. S. Dresselhaus, “Physical Properties of CarbonNanotubes,” Imperial College Press, London U.K. 1998, or A. Zettl“Non-Carbon Nanotubes” Advanced Materials, 8, p. 443 (1996)).

In a preferred embodiment, nanotubes of this invention comprisesstraight and bent multi-walled nanotubes (MWNTs), straight and bentdouble-walled nanotubes (DWNTs) and straight and bent single-wallednanotubes (SWNTs), and various compositions of these nanotube forms andcommon by-products contained in nanotube preparations such as describedin U.S. Pat. No. 6,333,016 and WO 01/92381, which are incorporatedherein by reference in their entirety.

The nanotubes of the instant invention have an outer diameter of lessthan 3.5 nm. In another preferred embodiment, nanotubes of the instantinvention have an outer diameter of less than 3.25 nm. In anotherpreferred embodiment, nanotubes of the instant invention have an outerdiameter of less than 3.0 nm. In another preferred embodiment, thenanotubes have an outer diameter of about 0.5 to about 2.5 nm. Inanother preferred embodiment, the nanotubes have an outer diameter ofabout 0.5 to about 2.0 nm. In another preferred embodiment, thenanotubes have an outer diameter of about 0.5 to about 1.5 nm. Inanother preferred embodiment, the nanotubes have an outer diameter ofabout 0.5 to about 1.0 rm. The aspect ratio may be between 10 and 2000.

In a preferred embodiment, the nanotubes comprise single walledcarbon-based SWNT-containing material. SWNTs can be formed by a numberof techniques, such as laser ablation of a carbon target, decomposing ahydrocarbon, and setting up an arc between two graphite electrodes. Forexample, U.S. Pat. No. 5,424,054 to Bethune et al. describes a processfor producing single-walled carbon nanotubes by contacting carbon vaporwith cobalt catalyst. The carbon vapor is produced by electric archeating of solid carbon, which can be amorphous carbon, graphite,activated or decolorizing carbon or mixtures thereof. Other techniquesof carbon heating are discussed, for instance laser heating, electronbeam heating and RF induction heating. Smalley (Guo, T., Nikoleev, P.,Thess, A., Colbert, D. T., and Smally, R. E., Chem. Phys. Lett. 243:1-12 (1995)) describes a method of producing single-walled carbonnanotubes wherein graphite rods and a transition metal aresimultaneously vaporized by a high-temperature laser. Smalley (Thess,A., Lee, R., Nikolaev, P., Dai, H., Petit, P., Robert, J., Xu, C., Lee,Y. H., Kim, S. G., Rinzler, A. G., Colbert, D. T., Scuseria, G. E.,Tonarek, D., Fischer, J. E., and Smalley, R. E., Science, 273: 483-487(1996)) also describes a process for production of single-walled carbonnanotubes in which a graphite rod containing a small amount oftransition metal is laser vaporized in an oven at about 1200° C.Single-wall nanotubes were reported to be produced in yields of morethan 70%. U.S. Pat. No. 6,221,330, which is incorporated herein byreference in its entirety, discloses methods of producing single-walledcarbon nanotubes which employs gaseous carbon feedstocks and unsupportedcatalysts.

SWNTs are very flexible and naturally aggregate to form ropes of tubes.The formation of SWNT ropes in the coating or film allows theconductivity to be very high, while loading is very low, and results ina good transparency and low haze.

The instant films provide excellent conductivity and transparency at lowloading of nanotubes. In a preferred embodiment, the nanotubes arepresent in the film at about 0.001 to about 1% based on weight.Preferably, the nanotubes are present in said film at about 0.01 toabout 0.1%, which results in a good transparency and low haze.

The instant films are useful in a variety of applications fortransparent conductive coatings such as ESD protection, EMI/RFIshielding, low observability, polymer electronics (e.g., transparentconductor layers for OLED displays, EL lamps, plastic chips, etc.). Thesurface resistance of the instant films can easily be adjusted to adaptthe films to these applications that have different target ranges forelectrical conductivity. For example, it is generally accepted that theresistance target range for ESD protection is 10⁶-10¹⁰ ohms/square. Itis also generally accepted that a resistance for conductive coatings forEMI/RFI shielding should be <10⁴ ohms/square. It is also generallyaccepted that low observability coatings for transparencies is typically<10³ ohms/square, preferably <10² ohms/square. For polymer electronics,and inherently conductive polymers (ICPs), the resistivity valuestypically are <10⁴ ohms/square.

Accordingly, in a preferred embodiment, the film has a surfaceresistance in the range of less than about 10¹⁰ ohms/square. Preferably,the film has a surface resistance in the range of about 10⁰-10¹⁰ohms/square. Preferably, the film has a surface resistance in the rangeof about 10¹-10⁴ ohms/square. Preferably, the film has a surfaceresistance in the range of less than about 10³ ohms/square. Preferably,the film has a surface resistance in the range of less than about 10²ohms/square. Preferably, the film has a surface resistance in the rangeof about 10⁻²-10⁰ ohms/square.

The instant films also have volume resistances in the range of about10⁻² ohms-cm to about 10¹⁰ ohms-cm. The volume resistances are asdefined in ASTM D4496-87 and ASTM D257-99.

The instant films demonstrate excellent transparency and low haze. Forexample, the instant film has a total transmittance of at least about60% and a haze value of visible light of about 2.0% or less. In apreferred embodiment, the instant films have a haze value of 0.5% orless.

In a preferred embodiment, the film has a total light transmittance ofabout 80% or more. In another preferred embodiment, the film has a totallight transmittance of about 85% or more. In another preferredembodiment, the film has a total light transmittance of about 90% ormore. In another preferred embodiment, the film has a total lighttransmittance of about 95% or more. In another preferred embodiment, hasa haze value less than 1%. In another preferred embodiment, film has ahaze value less than 0.5%.

Total light transmittance refers to the percentage of energy in theelectromagnetic spectrum with wavelengths less than 1×10⁻² cm thatpasses through the films, thus necessarily including wavelengths ofvisible light.

The instant films range from moderately thick to very thin. For example,the films can have a thickness between about 0.5 nm to about 1000microns. In a preferred embodiment, the films can have a thicknessbetween about 0.005 to about 1000 microns. In another preferredembodiment, the film has a thickness between about 0.05 to about 500microns. In another preferred embodiment, the film has a thicknessbetween about 0.05 to about 500 microns. In another preferredembodiment, the film has a thickness between about 0.05 to about 400microns. In another preferred embodiment, the film has a thicknessbetween about 1.0 to about 300 microns. In another preferred embodiment,the film has a thickness between about 1.0 to about 200 microns. Inanother preferred embodiment, the film has a thickness between about 1.0to about 100 microns. In another preferred embodiment, the film has athickness between about 1.0 to about 50 microns.

In another preferred embodiment, the film further comprises a polymericmaterial. The polymeric material may be selected from a wide range ofnatural or synthetic polymeric resins. The particular polymer may bechosen in accordance with the strength, structure, or design needs of adesired application. In a preferred embodiment, the polymeric materialcomprises a material selected from the group consisting ofthermoplastics, thermosetting polymers, elastomers and combinationsthereof. In another preferred embodiment, the polymeric materialcomprises a material selected from the group consisting of polyethylene,polypropylene, polyvinyl chloride, styrenic, polyurethane, polyimide,polycarbonate, polyethylene terephthalate, cellulose, gelatin, chitin,polypeptides, polysaccharides, polynucleotides and mixtures thereof. Inanother preferred embodiment, the polymeric material comprises amaterial selected from the group consisting of ceramic hybrid polymers,phosphine oxides and chalcogenides.

Films of this invention may be easily formed and applied to a substratesuch as a dispersion of nanotubes alone in solvents such as acetone,water, ethers, and alcohols. The solvent may be removed by normalprocesses such as air drying, heating or reduced pressure to form thedesired film of nanotubes. The films may be applied by other knownprocesses such as spray painting, dip coating, spin coating, knifecoating, kiss coating, gravure coating, screen printing, ink jetprinting, pad printing, other types of printing or roll coating.

A dispersion is a composition comprising preferably, but not limited to,a uniform or non-uniform distribution of two or more heterogeneousmaterials. Those materials may or may not chemically interact with eachother or other components of the dispersion or be totally or partiallyinert to components of the dispersion. Heterogeneity may be reflected inthe chemical composition, or in the form or size of the materials of thedispersion.

The instant films may be in a number and variety of different formsincluding, but not limited to, a solid film, a partial film, a foam, agel, a semi-solid, a powder, or a fluid. Films may exist as one or morelayers of materials of any thickness and three-dimensional size.

The substrate is not critical and can be any conductive ornon-conductive material, for example, metals, organic polymers,inorganic polymers, glasses, crystals, etc. The substrate for example,maybe, transparent, semi-transparent, or opaque. For example, thesubstrate may be a woven carbon or glass fabric to form a prepreg (resincoated fabric) wherein the instant conductive films enhance visualquality inspection of the prepreg. Alternatively, the substrate may bean electronic enclosure with a conductive film to render the surfaceconductive without significantly changing the appearance of theenclosure.

The instant films comprising nanotubes in a proper amount mixed with apolymer can be easily synthesized. At most a few routine parametricvariation tests may be required to optimize amounts for a desiredpurpose. Appropriate processing control for achieving a desired array ofnanotubes with respect to the plastic material can be achieved usingconventional mixing and processing methodology, including but notlimited to, conventional extrusion, multi-dye extrusion, presslamination, etc. methods or other techniques applicable to incorporationof nanotubes into a polymer.

The nanotubes may be dispersed substantially homogeneously throughoutthe polymeric material but can also be present in gradient fashion,increasing or decreasing in amount (e.g. concentration) from theexternal surface toward the middle of the material or from one surfaceto another, etc. Alternatively, the nanotubes can be dispersed as anexternal skin or internal layer thus forming interlaminate structures.

In a preferred embodiment, the instant nanotube films can themselves beover-coated with a polymeric material. In this way, the inventioncontemplates, in a preferred embodiment, novel laminates ormulti-layered structures comprising films of nanotubes over coated withanother coating of an inorganic or organic polymeric material. Theselaminates can be easily formed based on the foregoing procedures and arehighly effective for distributing or transporting electrical charge. Thelayers, for example, may be conductive, such as tin-indium mixed oxide(ITO), antimony-tin mixed oxide (ATO), fluorine-doped tin oxide (FTO),aluminum-doped zinc oxide (FZO) layer, or provide UV absorbance, such asa zinc oxide (ZnO) layer, or a doped oxide layer, or a hard coat such asa silicon coat. In this way, each layer may provide a separatecharacteristic.

In a preferred embodiment, the multi-layered structures have alternatinglayers of nanotube-containing and non-nanotube containing layers.

In a preferred embodiment, the nanotubes are oriented by exposing thefilms to a shearing, stretching, or elongating step or the like, e.g.,using conventional polymer processing methodology. Such shearing-typeprocessing refers to the use of force to induce flow or shear into thefilm, forcing a spacing, alignment, reorientation, disentangling etc. ofthe nanotubes from each other greater than that achieved for nanotubessimply formulated either by themselves or in admixture with polymericmaterials. Oriented nanotubes are discussed, for example in U.S. Pat.No. 6,265,466, which is incorporated herein by reference in itsentirety. Such disentanglement etc. can be achieved by extrusiontechniques, application of pressure more or less parallel to a surfaceof the composite, or application and differential force to differentsurfaces thereof, e.g., by shearing treatment by pulling of an extrudedplaque at a variable but controlled rate to control the amount of shearand elongation applied to the extruded plaque. It is believed that thisorientation results in superior properties of the film, e.g., enhancedelectromagnetic (EM) shielding.

Oriented refers to the axial direction of the nanotubes. The tubes caneither be randomly oriented, orthoganoly oriented (nanotube arrays), orpreferably, the nanotubes are oriented in the plane of the film.

In a preferred embodiment, the invention contemplates a plurality ofdifferentially-oriented nanotube film layers wherein each layer can beoriented and adjusted, thus forming filters or polarizers.

In a preferred embodiment, the invention also provides dispersionscomprising nanotubes. Preferably, the nanotubes have an outer diameterless than 3.5 nm. The instant dispersions are suitable for forming filmsas described herein. Accordingly, the instant dispersions may optionallyfurther comprise a polymeric material as described herein. The instantdispersions may optionally further comprise an agent such as aplasticizer, softening agent, filler, reinforcing agent, processing aid,stabilizer, antioxidant, dispersing agent, binder, a cross-linkingagent, a coloring agent, a UV absorbent agent, or a charge adjustingagent.

Dispersions of the invention may further comprise additional conductiveorganic materials, inorganic materials or combinations or mixtures ofsuch materials. The conductive organic materials may comprise particlescontaining buckeyballs, carbon black, fullerenes, nanotubes with anouter diameter of greater than about 3.5 nm, and combinations andmixtures thereof. Conductive inorganic materials may comprise particlesof aluminum, antimony, beryllium, cadmium, chromium, cobalt, copper,doped metal oxides, iron, gold, lead, manganese, magnesium, mercury,metal oxides, nickel, platinum, silver, steel, titanium, zinc, orcombinations or mixtures thereof. Preferred conductive materials includetin-indium mixed oxide, antimony-tin mixed oxide, fluorine-doped tinoxide, aluminum-doped zinc oxide and combinations and mixtures thereof.Preferred dispersion may also contain fluids, gelatins, ionic compounds,semiconductors, solids, surfactants, and combinations and mixturesthereof.

The present invention, thus generally described, will be understood morereadily by reference to the following examples, which are provided byway of illustration and are not intended to be limiting of the presentinvention.

EXAMPLES

Comparison of Electrical Properties for MWNT (Hyperion and Carbolex) andSWNT (CNI (Laser Ablated and HiPCO))

The nanotubes in Table 1 were sonicated for eight minutes into TitaniumSI-DETA (ceramer hybrid resin, this work has been repeated for otherresin systems like epoxy and urethane) and then cast onto a glass orpolycarbonate slide. A set of Hyperion MWNT was sonicated in toluenethen rinsed in IPA and added to the Titanium SI-DETA were it wassonicated for another 4 minutes. The thickness of the cast films is 0.5mils thick. TABLE 1 Hyperion Wt. % MWnT % T Bucky Nanotubes HyperionToluene Toluene USA CNI Dry Wt. MWnT % T Extracted Extracted MWnT* % TSWnT % T 0.04 2.2E+9 84.5 0.06 3.5E+7 73.5 0.08 3.5E+7 76.20.10 >1.0E+11 92 >1.0E+11 85.5 >1.0E+11 94.4 4.5E+7 80.2 0.20 >1.0E+1188.1 >1.0E+11 77.4 >1.0E+11 94.2 1.0E+7 70.0 0.30 >1.0E+11 88.7 >1.0E+1174.1 >1.0E+11 93.1 7.5E+6 59.4 10.40 >1.0E+11 85.7 >1.0E+11 92.5 1.7E+654.8 0.50 >1.0E+11 82.2 >1.0E+11 63.4 >1.0E+11 92 1.00 >1.0E+11 68.53.5E+9 37.5 >1.0E+11 84.7 2.00 >1.0E+11 46.9 6.0E+6 15.2 >1.0E+11 81.53.00 >1.0E+11 41.6 3.25E+6 5.4 >1.0E+11 79.8

As discussed above, U.S. Pat. No. 5,908,585 discloses a film having twoconductive additives. In this table they did not create a film with highenough conductivity to qualify as an ESD films (<10E10 Ohms/sq). Onlywhen they add a substantial (>20%) loading of conductive metal oxidedoes the films function as claimed. All claims are founded on this useof both fillers.

Optical Properties, Transmission, Color and Haze for Three Coatings.0.1%, 0.2%, and 0.3% SWNT in Ceramer Coating TABLE 2 Haze Test Resultsfor Si-DETA-50-Ti coatings on glass at 18 um thickness Sample ThicknessTotal Luminous Diffuse Name Number inches Haze % Transmittance(%) Trans% Blank 1 0.044 0.1 92.0 0.1 2 0.044 0.1 92.0 0.1 3 0.044 0.1 92.0 0.10.1% SWNT 1 0.044 3.2 85.2 3.8 2 0.044 3 85.0 3.5 3 0.044 3 85.2 3.50.2% SWNT 1 0.044 3.8 81.9 4.6 2 0.044 4.3 81.3 5.3 3 0.044 3.7 81.9 4.50.3% SWNT 1 0.044 5.7 76.8 7.4 2 0.044 5.5 77.3 7.1 3 0.044 5.6 76.9 7.3Color Scale XYZ 1 2 3 AVE BLANK C2 X 90.18 90.19 90.18 90.18 Y 91.9992.00 91.99 91.99 Z 108.52 108.53 108.52 108.52 F2 2 X 16.18 16.18 16.1816.18 Y 26.98 26.99 26.99 26.99 Z 124.83 124.84 124.83 124.83 A2 X101.05 101.06 101.05 101.05 Y 91.99 92.00 92.00 92.00 Z 32.67 32.6732.67 32.67 0.1% SWNT C2 X 83.31 83.13 83.23 83.22 Y 85.23 85.04 85.1585.14 Z 97.89 97.75 97.76 97.80 F2 2 X 15.01 14.97 14.99 14.99 Y 25.1825.12 25.16 25.15 Z 115.77 115.50 115.65 115.64 A2 X 93.87 93.65 93.7893.77 Y 85.38 85.18 85.30 85.29 Z 29.57 29.52 29.53 29.54 0.2% SWNT C2 X80.21 79.55 80.17 79.98 Y 81.93 81.25 81.89 81.69 Z 95.01 94.15 94.9694.71 F2 2 X 14.43 14.30 14.42 14.38 Y 24.19 23.99 24.18 24.12 Z 111.26110.32 111.20 110.93 A2 X 90.20 89.46 90.15 89.94 Y 82.04 81.37 82.0081.80 Z 38.65 28.40 28.64 31.90 0.3% SWNT C2 X 75.13 75.65 75.24 75.34 Y76.78 77.32 76.90 77.00 Z 88.29 88.96 88.42 88.56 F2 2 X 13.53 13.6213.55 13.57 Y 22.74 22.88 22.77 22.80 Z 104.30 105.02 104.46 104.59 A2 X84.63 85.20 84.74 84.86 Y 76.94 77.47 77.06 77.16 Z 26.65 26.85 26.6926.73

Referring to FIG. 1, a plot of conductivity verses thickness for SWNTcoatings is provided. Note that new HiPCO CNI nanotubes provide lowerresistance.

Conductivity Verses Humidity for SWNT Coatings

Referring to Table 3 and FIG. 2, humidity does not affect the electricalconductivity of the SWNT/Si-DETA coating. FIG. 2 shows the affect ofhigh humidity over an extended period of time. The resistance wasunchanged over a month at saturated conditions. TABLE 3 Percent DateTemperature Humidity Ohms/Square Nov. 4, 2000 23 40  1.2E+5 Nov. 6, 200023 6 1.38E+5 Nov. 7, 2000 23 98  4.0E+5 Nov. 8, 2000 23 98  3.8E+5 Nov.14, 2000 23 98 1.35E+5 Nov. 17, 2000 23 98 1.52E+5 Nov. 30, 2000 22 98 2.2E+5 Dec. 7, 2000 21 98  2.8E+5

Referring to FIG. 3, surface resistivity data for Si-DETA-50-Ti with0.3% SWNT cast on to a glass slide is shown. The test period was overeight days with long soak times at each temperature. Very littlehysteresis was observed, from starting values, when the sample wasremoved from the apparatus and returned to room temperature severaltimes during the test. Note that the sample turned dark brown andcracked once the temperature exceeded 300° C. It is also interesting tonote that even though the sample looked destroyed after testing it stillhave nearly the same resistivity as prior to testing. This test wasrepeated using a sample with lower loading of SWNT (0.2%) cast form thesame batch of ceromer resin, see FIG. 4. The dependence on test voltageis also depicted. The ASTM test voltage is 500V, preferred. Actualstatic charge is much higher, up to 20,000V. Apparently, the ceromer ESDcoating has reduced resistivity with increasing voltage. The peak at 50to 100° C. may be due to moisture. The present inventors have notedreduced magnitude during second cycle of testing the same specimen. Thevoltage dependence is shown in detail in FIG. 5.

Based on the foregoing, it is projected that the surface resistivity ofthe nanotubes will remain constant after exposure to temperaturesexceeding 800° C, and at temperatures exceeding 1000° C. Thus, thecoating provides substantially the same ESD protection even after hightemperature exposure.

FIG. 6 shows the percent nanotubes cast on glass slides labeled withresistance measurements.

ESD Coatings

Electrical conductivity to a resin system without adversely affectingthe other physical properties is demonstrated. This data presented inthis section was obtained using three polyimides; POLYIMIDE-1 (CP-1 fromSRS), POLYIMIDE-2 (CP-2 from SRS), and TPO (triphenyl phosphine oxidepolymer from Triton Systems, Inc.). Similar results to those presentedbelow, have been collected on other resins and are expected from mostother polymer resins useful for film forming and coatings applications.

Summary of Results

Electrical conductivity has been imparted to a resin system withoutadversely affecting other physical properties. Data presented in thissection demonstrate three polyimides; POLYIMIDE-1, POLYIMIDE-2, and TPO.Similar results to those presented below, have been collected on otherresins and are expected from most other polymer resins useful for filmforming and coatings applications.

Successful incorporation of SWNTs into ESD films and coatings are listedhere with a brief summary of some of the results obtained:

A) Electrical resistivity; concentration, and thickness of nanotubefilled films. Resistivity easily adjusted from 10² to 10¹² at anythickness greater than 1 micron. Resistivity through bulk or surface offilms demonstrated with very high optical clarity and low haze.

B) Thermal effect on conductivity. Resistivity insensitive totemperature and humidity from at least −78 to +300° C. Resistivitylowers with increasing voltage. Resistivity insensitive to temperaturecycling and soak.

C) Optical transparency of SWNT filled matrix for window and lensapplications. Transmission loss of only 10-15% for 25 micron thick filmswith bulk conductivity. Transmission loss of only 1-5% for thinner 2-10micron conductive films. Haze values typically <1%. Mechanical propertychanges to the resin and final films due to presence of nanotubes.Tensile, modulus, and elongation to break unaffected by addition ofnanotubes. Coefficient of thermal expansion unaffected by addition ofnanotubes. No other qualitative differences between films with orwithout nanotubes observed.

D) Processing of resin and films unaffected by incorporation ofnanotubes. Viscosity, surface tension, wetting, equivalent to unfilledresin. Casting, drying, curing, film parting, and final surfaceappearance identical. In special cases of high nanotube loading someviscosity increase is observed.

E) Formulation of the SWNT homogeneously throughout the matrix foruniform properties. Large area (2 ft. sq.) films have very uniformelectrical characteristics. Processing used in phase I is scalable usingcontinuous homogenizers and mixers. Some inclusions due in part toimpurities in nanotubes still present a challenge.

Each of these key areas is presented in detail following a briefdiscussion on experimental plan.

The films and coatings used for testing form two classes. The firstclass of films are those made for comparative properties testing betweenPOLYIMIDE-1, POLYIMIDE-2, and TPO films with and without nanotubes. Inthis matrix of films samples, all preparation conditions, procedures,and materials where identical for the films made with or withoutnanotubes. A uniform final film thickness of 25 microns was alsomaintained. The loading concentration of SWNTs was determined frompreliminary test films created with nanotube filling weight percentagebetween 0.03 to 0.30%. From this test, the films were standardized to0.1% to give films with resistivity between 10⁵-10⁹ Ohms/sq. During theconcentration test films with resistivity from 50 Ohms/sq to over 10¹²Ohms/Sq were able to be made. Lastly, the film thickness was selected tobe 1 mil (25 um) since current application make use of this thicknessand based on observations that resistivity, at a set concentration ofnanotubes, does not vary with thickness unless film is below 2 microns.This resulting set of specimens was used in a test matrix comparing: 1)electrical resistivity at various temperatures, 2) optical transmittanceand haze, 3) mechanical properties of tensile, modulus, elongation, and4) coefficient of thermal expansion (CTE). The preparation and resultsof testing the films in this matrix are presented as listed above.

The second class of films and coatings for testing were prepared byvarious means and represent special coatings and films which demonstratethe wide variety of properties attainable using this nanotechnologyenhancement to these resins. For example, these samples includemeasurement of resistivity as a function of the film thickness andnanotube loading level. The methods used for preparation of thesespecial demonstrations are presented.

Preparation and Test Results for Films in Comparative Matrix

The materials used were POLYIMIDE-1 and POLYIMIDE-2, and TPO. BothPOLYIMIDE-1 and POLYIMIDE-2 were cast at a final concentration of 15%while TPO was cast at a final concentration of 20% in NMP. To preparethe resins for casting, each resin was placed in a three-neck roundbottom flask with enough NMP to make more concentrated 20% solution forPOLYIMIDE-1 and POLYIMIDE-2 and a 25 % solution for TPO. Thisconcentrate is later reduced by the addition of NMP and nanotubes. Theresins were made in large batches, purged with nitrogen and stirred at30 RPM for 18 hours. Each batch of resin was split in half and placedinto two fresh flasks. Then two aliquots of NMP were placed in smalljars for cutting the concentration of resin to casting viscosity. SWNTswere weighed out and added to pure NMP. The SWNTs and NMP were sonicatedfor 12 minutes. To one flask of resin concentrate, an aliquot of pureNMP was added to the concentrate while the other half of the resinsolution an aliquot of NMP containing SWNTs was added. Both flasks werestirred at 30 RPM for half an hour, filtered and placed in jars forcasting. Through the task of preparing the resins for casting, attentionto stirring, mixing and other details were standardized to keepprocessing of the virgin and 0.1% SWNT resins the same.

The samples were cast onto ¼ inch thick glass panels that were cleanedwith soap and water and then rinsed in pure water and allowed to dry.The glass was washed and with methanol and a lint free cloth. When themethanol dried the samples were cast two inches wide using a castingknife to make a final thickness of 1 mil final thickness. ForPOLYIMIDE-1 and POLYIMIDE-2 a 12.5 mil casting thickness was used whileTPO required 10-mil casting to achieve 1 mil. The cast samples were diedat 130° C. overnight and then at 130° C. under vacuum for an hour. Thethin samples prepared for optical testing were not removed from theglass but dried and heated like all the other coatings. The films werethen floated off the glass by using purified water, to reduce waterspots. After drying, the samples were tested for residual solvents usinga TGA. The remaining solvent was about 10, which was too high. Thesamples were then taped on the glass panels using Kapton tape and heatedto 130° C. under vacuum for 18 hours. Using the TGA again to check forsolvent content it was found that the coatings were reduced to about3-6% solvent. The samples were placed back into the oven and heated to160° C. under vacuum for 18 hours. After this heating process thesolvent levels were below 2% and used for testing.

The following test results were obtained: 1) electrical resistivity atvarious temperatures; 2) optical transmittance and haze; 3) mechanicalproperties of tensile, modulus, elongation; and 4) coefficient ofthermal expansion (CTE).

Resistivity in Comparative Matrix as a Function of Temperature, Voltage,and Humidity.

Background:

To impart the conductive path throughout a structure, athree-dimensional network of filler particles was required. This isreferred to as percolation threshold and is characterized by a largechange in the electrical resistance. Essentially, the theory is based onthe agglomeration of particles, and particle-to-particle interactionsresulting in a transition from isolated domains to those forming acontinuous pathway through the material. Nanotubes have a much lowerpercolation threshold than typical fillers due to their high aspectratio of >1000 and high conductivity. As and example, the calculatedpercolation threshold for carbon black is 3-4% while for typical carbonnanotubes the threshold is below 0.04% or two orders of magnitude lower.This threshold value is one of the lowest ever calculated and confirmed.(See J. Sandler, M. S. P. Shaffer, T. Prasse, W. Bauhofer, A. H. Windleand K. Schulte, “Development of a dispersion process for catalyticallygrown carbon nanotubes in a epoxy matrix and the resulting electricalproperties”, University of Cambridge, United Kingdom, and the TechnicalUniversity Hamburg-Hamburg, Germany).

The high conductivity imparted when NT's are dispersed in a polymer atlow concentrations (0.05 to 2-wt. %) is not typically observed in afilled material. This is one of the most attractive aspects to using NTto make conductive materials. For a typical filled system, likepolyaniline (PAN) particles in a polymer matrix, a 6 to 8% volumefraction is required to reach percolation threshold for conductivity.Even when PAN is solution blended the loading exceeds 2 wt. %. Another,more common example is found in ESD plastics used in the electronicsindustry were polymers are filled with carbon black to a loading of 10to 30-wt. %.

The high conductivity at low concentration is due to the extraordinarilyhigh aspect ration of SWNTs and the high tube conductivity. In fact, theelectrical conductivity of individual tubes has been measured anddetermined to exhibit metallic behavior.

Electrical Resistivity and Thermal Stability.

To demonstrate the thermal stability through a wide range oftemperatures we mounted samples from each film in the test matrix ontoglass slides using Kapton tape. These slides were placed in anenvironmental test chamber with leads attached to silver-metal paintedstripes on each of the three types, POLYIMIDE-1, POLYIMIDE-2, and TPO.The results showing how each of the three films resistivity varied withtemperature from −78 to +300° C., are presented in FIG. 8.

The results indicate that electrical resistivity in all three films isinsensitive to a wide range of temperatures. The relative value ofresistivity between the films is not important since it can be adjustedeasily by changing the concentration of the tubes.

However, in general TPO has a high resistivity at a given nanotubeconcentration in all the samples made in the phase I. This data alsoindicates that imparting conductivity to polymer by addition of SWNTswill produce a film with excellent thermal stability, at least as goodas the base resins. These films were cycled through this test severaltimes without any notable change in resistivity. In addition, we leftthen to soak for a period of 63 hours in air at 250° C. to observe thelong-term stability as shown in Table 4 below: TABLE 4 Resistivity(Ohms/sq.) vs. Time Hours at 250 C. POLYIMIDE-1 POLYIMIDE-2 TPO 0 3.0E+65.4E+6 6.3E+6 63 4.4E+6 6.1E+6 7.8E+6

Also of interest was the relationship between test voltage and measureresistivity. The resistivity was calculated by holding the test voltageconstant and recording the current across the sample using ohms law.POLYIMIDE-1 coated on glass with 0.1% SWNTs was tested from 1 Volt to 20KV, with the calculated resistivity, normalized to Ohms/sq, plotted inFIG. 9. This graph shows that the resistance of these films reduces withincreasing voltage. This is also observed at elevated temperatures. Froma design stand point, this meant those films tested using low voltagemeters is adequate, since the resistance was only going to reduce is thefilm is subject to higher voltage in the application. In fact thesecarbon nanocomposite films may be developed for lightening protection.

To test thermal stability, samples of each of the six films in the testmatrix were scanned by TGA and DSC to evaluate how they behave with andwithout nanotube present. The percent weight loss at 350° C. and theglass transition temperature was recorded. See the Tables 6 and 7 belowfor results: TABLE 6 TGA Data on POLYIMIDE-1, POLYIMIDE-2 and TPO filmswith and with nanotubes % Weight Sample loss Description @ 350° C.Virgin 1.57 POLYIMIDE-1 POLYIMIDE-1 1.46 w/SWnT Virgin 3.50 POLYIMIDE-2POLYIMIDE-2 4.57 w/SWnT Virgin TPO 3.64 TPO w/SWnT 4.65

TABLE 7 DSC Data on POLYIMIDE-1, POLYIMIDE-2, TPO Films Glass TransitionSample Temperature T_(g) Reported T_(g) Description (° C.) (° C.)POLYIMIDE-1 248.3 263 Virgin POLYIMIDE-1 249.7 w/SWnT POLYIMIDE-2 163.8209 Virgin POLYIMIDE-2 162.4 w/SWnT TPO Virgin 172.4 N/A TPO w/SWnT186.8

The decrease in the TGA and T_(g) of the films is a result of residualNMP trapped in the film. The TPO resin did not give a clean or good DSCcurve until thermally cycled a couple times.

Summary of Electrical Test Results.

Films have electrical resistivity much lower than required for ESDapplications and can be easily designed for any level of electricalresistance above a 100 Ohms/sq. using very low loading level ofnanotubes. Electrical properties are insensitive to temperature,humidity, ageing. The presence of the nanotube does not harm the otherthermal properties of the films.

Optical Transmittance and Haze.

SWNTs are excellent additives to impart conductivity to polymericsystems and consequently function well in an ESD role. However, forapplication to optics and windows, the resulting films or coatings mustalso be transparent. Samples of each film made for the comparative testmatrix were tested using ASTM D 1003 “Standard Test Method for Haze andLuminous Transmittance of Transparent Plastics” This test method coversthe evaluation of specific light-transmitting andwide-angle-light-scattering properties of planar sections of materialssuch as essentially transparent plastic. A procedure is provided for themeasurement of luminous transmittance and haze. We also tested thinnerfilms made from the same resin batch. This data is presented in theTable 8 below. For comparison, the same films were tested for % T atfixed frequency of 500 nm using a Beckman UV-Vis spectrometry on bothglass, see Table 9, and as free standing films, see Table 10. TABLE 8ASTM D1003-00B, optical haze, luminous and diffuse transmittance datafor films with and without nanotubes. Note all thee films are conductivein the ESD range Ohms Total Thickness per Luminous Diffuse SampleIdentification Microns Square Haze % Trans % Trans % Test Matrix Films,Free Standing POLYIMIDE-2 Virgin film 27 >1.0 × 10¹² 1.4 88.9 1.6POLYIMIDE-2 With 0.1% 27   1.6 × 10⁶  3.1 62.7 5.0 SWnT film TPO Virginfilm 30 >1.0 × 10¹² 1.5 86.8 1.7 TPO With SWnT film 30   5.0 × 10⁸  1.070.7 1.4 POLYIMIDE-1 Virgin film 25 >1.0 × 10¹² 0.7 90.2 0.8POLYIMIDE-1With SWnT 25   1.4 × 10⁷   1.1 64.8 1.7 film ThinFilms/Coatings on Glass Blank NA NA 0.3 88.5 NA POLYIMIDE-1 Virgin4 >1.0 × 10¹² 0.1 99.2 0.1 POLYIMIDE-1 With 0.1% 4   3.0 × 10⁸  0.3 93.60.3 SWnT POLYIMIDE-1 Virgin 12 >1.0 × 10¹² 0.3 99.0 0.3 POLYIMIDE-1 With0.1% 12   1.9 × 10⁷  0.4 85.0 0.4 SWnT

POLYIMIDE-1 was cast onto glass substrates with and without SWNTs at 2and 6 mils thick. An additional ultrathin sample was prepared usingPOLYIMIDE-1 compounded with 0.3% SWNTs and cast at 0.5 mil thick. Thesesamples were tested on the UV-Vis spectrometer for percent transmissionat 500 nm, an industry standard for comparison. The glass was subtractedout of each sample. Table 9 presents the optical and resistivity datafor these samples cast on glass. The same tests were run on POLYIMIDE-2and TPO, with very similar results. TABLE 9 POLYIMIDE-1 on glass % T @Resistivity in Sample Description 500 nm Ohms/Sq. POLYIMIDE-1 with 0.1%77.3 3.0E+8 SWnT at 4 um POLYIMIDE-1 with 0.1% 75.2 1.9E+7 SWnT at 12 umVirgin POLYIMIDE-1 at 4 um 83.7 >10¹³ Virgin POLYIMIDE-1 at 12 um 89.2>10¹³

Another set of samples were cast at the same thickness and removed fromthe glass. The freestanding films were also analyzed using the UV-Vis at500 nm. Table 10 represents the results of the freestanding films. TABLE10 Freestanding POLYIMIDE-1 % T @ Resistivity in Sample Description 500nm Ohms/Sq. POLYIMIDE-1 with 0.1% 77.3 3.0E+8 SWnT at 4 um POLYIMIDE-1with 0.1% 75.2 1.9E+7 SWnT at 12 um Virgin POLYIMIDE-1 at 4 um 83.7>10¹³ Virgin POLYIMIDE-1 at 12 um 89.2 >10¹³

Summary of Optical Test Results.

The optical testing of these ESD films in the test matrix demonstratesexcellent transmission with low loss. Even more exciting are the resultsof thin film and bi-layer experiments where optical properties were thefocus and result in near colorless (>95% T) films and coatings. Withsuccessful demonstration of optically clear, low resistivity films, thenext step was to confirm that these films have the same or bettermechanical properties as those not enhance with nanotubes.

Mechanical Properties of Tensile, Modulus, Elongation.

The use of these films inmost application requires good mechanicalproperties. In this section, it is demonstrated that the presence ofnanotube to impart the ESD characteristic does not adversely affect themechanical properties of these polymer films. To that end, each type offilm with and with out nanotube present was tested for tensile strength,tensile modulus, and elongation at break. The results of these tests arein Table 11 and graphed in FIG. 10.

Coefficient of Thermal Expansion (CTE).

SWNTs' ability to impart ESD characteristics does not adversely affectthe coefficient of thermal expansion (CTE) properties of polymer films.To that end, each type of film with and with out nanotube present wastested. The CTE tests were conducted using Universal Testing Machinefrom SRS. The testing was conducted on 6 samples of film: VirginPOLYIMIDE-1, POLYIMIDE-1 with SWNT, Virgin POLYIMIDE-2, POLYIMIDE-2 withSWNT, Virgin TPO, and TPO with SWNT.

Each sample was first mounted onto a strip of 5 mil Kapton since thesamples alone were slightly too short to be placed on the fixturesproperly. Once the sample was fixed to the machine, the strain gageclamps were placed onto the film using a standard 4″ gage length. Thefilm was then loaded with approximately 15 grams, which would provide asuitable stress to initiate elongation during heating but not permanentdeformation.

The POLYIMIDE-1 and POLYIMIDE-2 samples behaved as expected throughoutthe temperature range. The TPO samples behaved irregularly as comparedto the polyimide. Initially, the samples appeared to shrink when heatwas first applied then would grow normally as the temperature increased.The behavior seemed typical for the TPO VIR trial 1 on the ramp upwardonce the film normalized. Interestingly, the TPO material followed adifferent profile on the temperature ramp down and actually decreased insize before growing back to its original size. Another interestingbehavior is that the TPO material seemed to change size if left to soakat 177 C (350° F.) for any length of time. The virgin TPO shrank whensoaked at 177° C. while the TPO with SWNTs grew when soaked at 177° C.Since the behavior was the same for both trials, it was determined thatneither operator error nor instrument error was at fault. All CTEmeasurements fell within 10% of known values and are presented in Table11 and in FIG. 11. TABLE 11 The CTE values for each material MaterialCTE (ramp up) CTE (ramp down) POLYIMIDE-1 53.27 ppm/C. 57.18 ppm/C.POLYIMIDE-1 with SWnT 56.87 ppm/C. 55.58 ppm/C. POLYIMIDE-2 63.38 ppm/C.64.45 ppm/C. POLYIMIDE-2 with SWnT 56.00 ppm/C. 56.43 ppm/C. TPO(trial1) 55.42 ppm/C. 57.04 ppm/C. TPO with SWnT (trial1) 53.81 ppm/C.56.13 ppm/C. TPO (trial2) 50.70 ppm/C. 57.60 ppm/C. TPO with SWnT(trial2) 60.86 ppm/C. 55.78 ppm/C.

Summary of CTE Testing

As with the tensile properties, the CTE properties of these films weregenerally unchanged by the addition of nanotubes. This will permit theuse of these other polymers enhanced by the addition of nanotubes forcoating and multilayer applications were CTE matching is important forbonding and temperature cycling.

Results Obtained from exploratory Films and Coatings.

In this section are provided those results obtained from films andcoating made from the same three resins, however, in these samples filmthickness and nanotube concentration were not held fix. Samples weregenerated to demonstrate the ease at which very high clarity, highconductivity coatings and films can be produced using Nano ESDtechnology. In brief, the following samples were prepared and presentedin the subsequent subsections of the proposal:

High clarity 1-2 micron thick coatings on glass with high loading levelsof (0.2 and 0.3%) nanotubes.

Bilayer films, where very thin, high nanotube loading level is layeredon standard thickness films.

Special polymer wrapped SWNT layered on 1 mil films.

High Clarity ESD Films

It is possible to obtain a highly absorbing film by increasing thenanotube concentration. A 1.5% loading level of multiwalled nanotubes inpolymer matrix is black and dull in appearance. In contrast, an 8-micronthick polymer coating loaded with 0.2% SWNTs is still conductive yetnearly colorless as depicted in FIG. 12. This coating was formed bycasting a solution of POLYIMIDE-1 with 0.3% SWNTs @ 1.5 μm finalthickness. It has a resistivity of 10⁸ Ohms sq with transparency 96% Twith haze of 0.6%.

This excellent coating demonstrates that by manipulating theconcentration and coating thickness excellent optical and electricalproperties can be obtained in the same film. For comparison, the samesample was tested in our UV-Vis spectrometer at 500 nm. The glasscomplicates the results since the ESD layer acts as an antireflectivecoating to the glass and alters the reflective components contributionto the transmission result. Nevertheless, this coating demonstrates thepotential for very high clarity ESD coatings. TABLE 12 Transmission at500 nm for thin 0.3% POLYIMIDE-1 coating on glass Sample % T @ 500 nm w/Resistivity in Description glass subtracted Ohms/Sq. Ultrathin monolayerof 83.8 3E+8 POLYIMIDE-1 with 0.3% SWnT 0.5 mil cast Blank piece ofglass 88.8 >10¹³

To reduce optical absorbance in nanocomposite conductive films thecoating can be formed from a thin monolayer of high concentrationnanotubes. Several other techniques have also been demonstrated toachieve the same high optical transparency while maintaining highelectrical conductivity in the film. Two of the most successful rely onthe same concept just shown, they are: 1) the use of bi-layers and 2)ultra thin polymer wrapped nanotubes.

Bi-Layer and Special Ultra Thin ESD Films.

A natural extension of the thin coating method for high optical claritycoatings, is to form a bi-layer free standing film by cast the thin 1 μmlayer first on glass and then over coating with the thicker, 25 um layerof virgin resin. The resulting film has a conductive surface withoutconductivity through the thickness. We made films from the TPO resin todemonstrate the concept. The specifications for this film are providedin Table 13.

Nanotube concentration was increased to almost 50% in the conductivelayer. This was done by modifying the nanotubes with a coating ofpolyvinylpyrrolidone (PVP). This is also referred to as wrapping thenanotubes with a helical layer of polymer. To accomplish this, SWNTswere suspended in sodium dodecy sulfate and PVP. This solution was thenincubated at 50° C. for 12 hours and then flocculated with IPA. Thesolution is centrifuged and washed in water three times and thensuspended in water. The resulting nanotubes are water soluble and easilysprayed or cast onto any surface. This solution was spray coated ontovirgin films to create a fine coating (<1 um thick) that has ESDproperties and is very clear and colorless.

The resulting coating can be coated with a thin binder while stillremaining conductive or coated with a thicker layer to make freestanding films. Using this technique, coatings with a resistivity downto 100 Ohms were generated.

Although only a few exemplary embodiments of the present invention havebeen described in detail in this disclosure, those skilled in the artwho review this disclosure will readily appreciate that manymodifications are possible in the exemplary embodiments (such asvariations in sizes, structures, shapes and proportions of the variouselements, values of parameters, or use of materials) without materiallydeparting from the novel teachings and advantages of the invention.Accordingly, all such modifications are intended to be included withinthe scope of the invention as defined in the appended claims.

Other substitutions, modifications, changes and omissions may be made inthe design, operating conditions and arrangement of the preferredembodiments without departing from the spirit of the invention asexpressed in the appended claims.

Additional advantages, features and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, and representativedevices, shown and described herein. Accordingly, various modificationsmay be made without departing from the spirit or scope of the generalinventive concept as defined by the appended claims and theirequivalents.

All references cited herein, including all U.S. and foreign patents andpatent applications, all priority documents, all publications, and allcitations to government and other information sources, are specificallyand entirely hereby incorporated herein by reference. It is intendedthat the specification and examples be considered exemplary only, withthe true scope and spirit of the invention indicated by the followingclaims.

As used herein and in the following claims, articles such as “the”, “a”and “an” can connote the singular or plural.

1-41. (canceled)
 42. A multi-layered structure comprising: anelectrically conductive film comprising a plurality of nanotubes with anouter diameter of less than 3.5 nm; and a polymeric layer disposed on atleast a portion of said electrically conductive film.
 43. Themulti-layered structure of claim 42, wherein said nanotubes have anouter diameter of about 0.5 to 3.5 nm.
 44. The multi-layered structureof claim 42, wherein said nanotubes are selected from the groupconsisting of single-walled nanotubes (SWNTs), double-walled nanotubes(DWNTs), multi-walled nanotubes (MWNTs), and mixtures thereof.
 45. Themulti-layered structure of claim 42, wherein said nanotubes aresubstantially single-walled nanotubes (SWNTs).
 46. The multi-layeredstructure of claim 42, wherein said nanotubes are present in said filmat about 0.001 to about 1% based on weight.
 47. The multi-layeredstructure of claim 42, wherein the film has a volume resistances in therange of about 10⁻² ohms/cm to about 10¹⁰ ohms/cm.
 48. The multi-layeredstructure of claim 42, wherein the film is in the form of a solid film,a foam, or a fluid.
 49. The multi-layered structure of claim 42, furthercomprising a polymeric material, wherein the polymeric materialcomprises a material selected from the group consisting ofthermoplastics, thermosetting polymers, elastomers, conducting polymersand combinations thereof.
 50. The multi-layered structure of claim 42,further comprising a polymeric material, wherein the polymeric materialcomprises a material selected from the group consisting of ceramichybrid polymers, phosphine oxides and chalcogenides.
 51. Themulti-layered structure of claim 42, further comprising a polymericmaterial wherein the nanotubes are dispersed substantially homogenouslythroughout the polymeric material.
 52. The multi-layered structure ofclaim 42, further comprising a polymeric material wherein the nanotubesare present in a gradient fashion.
 53. The multi-layered structure ofclaim 42, further comprising a polymeric material wherein the nanotubesare present on a surface of said polymeric material.
 54. Themulti-layered structure of claim 42, further comprising a polymericmaterial wherein the nanotubes are formed in an internal layer of saidpolymeric material.
 55. The multi-layered structure of claim 42, furthercomprising an opaque substrate, wherein the nanotubes are present on asurface of said opaque substrate.
 56. The multi-layered structure ofclaim 42, further comprising an additive selected from the groupconsisting of a dispersing agent, a binder, a cross-linking agent, astabilizer agent, a coloring agent, a UV absorbent agent, and a chargeadjusting agent.
 57. The multi-layered structure of claim 42, whereinthe film has a total transmittance of at least about 60%.
 58. Themulti-layered structure of claim 42, wherein said film has a thicknessbetween about 0.005 to about 1,000 microns.
 59. The multi-layeredstructure of claim 42, wherein the nanotubes are oriented.
 60. Themulti-layered structure of claim 42, wherein the nanotubes are orientedin the plane of the film. 61-72. (canceled)